1. Field of Invention
The invention relates to the technology associated with an optical disk, and more particularly to a method for identifying a type of an optical disk.
2. Related Art
Recently, the technology grows rapidly, and optical disks, such as compact disks (CD) and a digital versatile disks (DVD), are getting more and more popular. Because the CD and DVD are designed for laser with different wavelengths and have different reflective indexes, the controller must download different parameters to access different types of disks. At this time, it is very important to correctly identify the type of the disk. This is because the ability of playing the disk will be deteriorated if the controller loads the wrong parameters. In addition, different types of optical disks have different written data formats, so the system must first identify the type of the disk to correctly load the parameters to read the disk or write the data into the disk.
The DVD may be categorized into various types including DVD-ROM, DVD+R/RW, DVD-R/RW and DVD-RAM. Each type may be classified into three states including a finalized state, an un-finalized state and an empty state.
In the conventional art, there are several methods for identifying the type of the DVD, and the methods will be described in the following.
The U.S. Patent Publication No. 2005/0265188 discloses a method for identifying the disk as the DVD-ROM, DVD+R or DVD-R according to the frequency of the wobble signal when the disk is read. In this method, a set of default parameters is set in a controller, then the frequency of the wobble signal on the DVD is obtained by reading, and then the type of the disk is identified according to the predetermined threshold value of the frequency. No wobble signal exists on a typical DVD-ROM disk, the frequency of the wobble signal on the DVD+R disk is 817.4 KHz, and the frequency of the wobble signal on the DVD-R disk is 140.6 KHz. Because the difference of the above frequency is obvious, this method can indeed identify the type of the disk.
However, this method has the drawback that the optical drive has to first track on and then read the frequency of the wobble signal. If the quality of the disk is too bad or data has been recorded on the disk, the wobble signal will have a lot of noise, which may interfere the precision of identifying the disk. In addition, before the frequency of the wobble signal is read, the optical drive has to work according to one set of default parameters, and the loaded parameters may not certainly suitable for any disks. If the quality of the disk is too bad, other sets of parameters will have to be tried to read the disk. Thus, the time period of reading the data on the disk is increased.
The U.S. Patent Publication No. 2005/0265187 discloses a method for identifying the disk as DVD+R or DVD-R according to the peak-to-peak voltage of the wobble signal on the disk. In this method, the default DVD-R parameters are first set in the controller, and then the wobble signal on the DVD is read. A threshold value is set to identify the type of the disk according to the level of the read wobble signal. Because a land pre pit (LPP) signal is pre-formed between grooves in the wobble signal of DVD-R, the level of the wobble signal is typically higher than that of DVD+R, and the disk is identified as DVD+R or DVD-R according to this concept. When the peak-to-peak voltage of the wobble signal is higher than a predetermined threshold value, the read optical disk is identified as DVD-R. When the peak-to-peak voltage of the wobble signal is lower than the predetermined threshold value, the read optical disk is identified as DVD+R.
Similarly, this method has the drawback that the optical drive has to first track on to read the wobble signal. In addition, the major problem is that the voltage level of the read wobble signal changes as the reflective index of the disk changes. In one specific condition, the DVD+R disk may have the higher reflective index so that the read level of the wobble signal is higher than the predetermined threshold value and the optical drive incorrectly identifies DVD+R as DVD-R. On the contrary, the DVD-R may be incorrectly identified as DVD+R. Thus, this method cannot be easily applied to the optical drive.
Taiwan Patent No. 1272580 (U.S. Pat. No. 6,778,479) discloses a method for identifying the type of the disk by reading the data storage format in the lead-in zone. This is because the basic information, including the type of the disk or the starting address and the ending address of the data in the disk, is stored in the lead-in zone of the disk. This method is to read the data in the lead-in zone on the optical disk after the optical drive is turned on, and thus to identify the type of the disk.
Similarly, this method has the drawback that the data in the lead-in zone cannot be read after the optical drive is turned on. Because the type of the disk is unknown, the optical drive has to read the data according to one default set of parameters. If the parameters loaded into the controller are not suitable for the disk in the optical drive, another set of parameters has to be re-loaded into the controller of the optical drive and the optical drive tries to read the data on the disk until the suitable parameters are loaded. Consequently, the time of reading the disk is inevitably increased. In addition, the disk type field in the lead-in zone of the DVD+R disk may be filled by the user. So, the user may fill this field with other types of disks in order to enhance the compatibility of this DVD+R. Thus, the optical drive may incorrectly identify the type of the disk.